During the drilling operations when a borehole is drilled through underground formations the drill string undergoes considerable abrasion during rotation within the borehold and/or the well casing. The abrasion is amplified when the drilling mud contains abrasive formation particles being flushed out of the drilling area by the drilling mud. The wear resulting from this abrasion often occurs on the shouldered areas of the tool joints and contributes greatly to a very rapid failure of the highly stressed thread areas of said tool joints.
Methods of slowing or reducing this wear involved fusing a layer of cast tungsten carbide particles in an alloy steel matrix. This resulted in an extended useful life of the tool joint but in many instances gave rise to a second detrimental effect which was a higher than normal rate of wear on the inside of the well casing. Later, it was found that a layer of mild steel alloy on top of a layer of large sintered tungsten carbide particles would greatly reduce the wear in the casing while extending the life of the tool joint. When offshore drilling became very prevalent in the industry, the single hardbanding procedure and the hardbanding procedure with a mild steel overlay resulted in an extended life for the tool joint which, though better than a plain steel joint, still left a lot to be desired.
Due to the expense and time involved in pulling drilling strings from offshore wells and shuttling new or resurfaced drill string components to the site from somewhere onshore, the wear and tear on drill strings became an even greater consideration. Attempted solutions involved placing thicker bands of hardsurfacing material on the tool joints. Unfortunately, this failed to solve the problem since the cast tungsten carbide particles are extremely brittle and therefore subject to spalling. Spalling is the failure of a hard brittle material during high point loading in compression.
The present invention provides a much thicker hardbanding application with accompanying extended life of the tool joint without increased susceptibility to failure due to spalling. This is achieved by utilizing multiple layers of sintered tungsten carbide particles in a steel matrix which provides a thicker overall surface of hardbanding material while the tougher sintered tungsten carbide particles are resistent to spalling.